"Rationality" -- or, really, just a thoughtful attitude -- has some major advantages in relationships, I've found. Some important relationship skills that require rationality:
"If I ever cheated on you -- not that I would -- I would use a condom." You need a rational person to say this, and a rational person to hear it. An irrational person would never want to consider the possibility of cheating, and so wouldn't want to think of contingency plans; such a person might be offended by the very suggestion that a bad situation might happen. In the same vein, rational couples can discuss things like "if my business fails," "if we break up," "if this crazy feeling of limerence fades," and so on. You can't deal with bad contingencies well if you can't think about them or discuss them at all.
People are different. Something could matter a lot to your partner that doesn't matter at all to you. Or vice versa. You can make each other happier if you can put effort into the things that the other person is passionate about even when you can't imagine feeling that way yourself. This is also a great way to diffuse fights before they even start; before you assume your partner has a nasty thought or attitude, find out what he's actually thinking. It can be surprising.
It's a rationalist skill just to be able to notice what your significant other does and predict that he'll keep doing it. So many relationship problems stem from the failure to notice patterns. Notice a behavioral pattern and you can learn to trust someone, learn his strengths and weaknesses, or learn to do what consistently makes him happier.
Some stereotypes are roughly true in a statistical sense -- people like high status and attractiveness in their mates, for example. If you want to keep a relationship going well, you should try to do things that statistically make relationships go well. On the other hand, people are individuals, and if it's a good idea to modify yourself to be different from the statistical majority in some way, you can and should. Statistics are evidence, but not destiny.
Rationalists tend to have the attitude that the world is interesting. This means you will never be boring company. It also means you'll be willing to seek out new experiences with your partner.
I never hear "judgment" among the top-ten qualities people desire in their partners, but I think it's more important than people realize. You really want to be with someone whose judgment you can trust and whose opinions you can respect. That doesn't mean "sober and boring," it means that you could trust your partner to be responsible for a choice that would affect your life profoundly (and that often happens in long-term relationships). Rationalists, if they're doing it right at all, have better judgment.
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Recently I asked for feedback on two versions of a new post, 'Rationality Lessons from Romance'. 'Version 2' was my original draft. 'Version 1' was a more recent draft edited in response to comments from a collaborator. We wanted to test whether my collaborator's comments genuinely improved the post. Version 2 now sits at 1 upvote and version 1 now sits at 16 upvotes, and I take this to be some evidence in favor of the hypothesis that my collaborator's comments improved the post.
My thanks to those who participated in that experiment; we got the information we wanted!
Thanks also to those of you who provided feedback on either version of the post. Most comments were critical, but this is often the case even with massively upvoted posts like Build Small Skills in the Right Order. My hope is that relationships posts on Less Wrong merely need to be better and more sensitive to a wide variety of sensitivities than my first attempt was, not that sex and relationships are inherently mind-killing topics. There is an amazing interplay between rationality and relationships, and I feel it would be a shame to leave them unexplored.
So I'm trying to learn how LessWrongers can discuss relationships productively.
One difficulty in extracting lessons from the feedback on 'Rationality Lessons from Romance' is that different people had different complaints. Some were 'seriously skeeved-out' by the overtly personal nature of the post, even though earlier posts of a similar personal nature have fared well on Less Wrong, and even though others didn't mind the personal-ness of the post. Some didn't like the promotion of polyamory, others didn't mind. Some thought my interactions with women were unethical, others didn't. Some disagreed with a premise of the post, that sexual jealousy and monogamy are suboptimal for some people. Some felt the brief lessons pulled out from the stories were effective, others didn't. Some thought I was, like Socrates, being skewered for looking at things with too much clarity, others thought my post was weird and confusing.
I may try to rewrite 'Rationality Lessons from Romance', incorporating as much of the feedback as I can. In the meantime, I'd like to ask the Less Wrong community to very different questions: